Preparation of nitride and carbide from inorganic-organic polymer complex

ABSTRACT

Nitrides and carbides are prepared by intercalating a monomer, a starting material of condensate, or a prepolymer into the interlamellar spaces or the vacant spaces of the crystalline structure of a natural mineral or an inorganic compound to prepare an intercalated compound and baking the intercalated polymer compound at a temperature in the range of 1100°-1700° C. under a nitrogen or reducing atmosphere. The present invention provides a method for readily preparing nitrides and carbides having the increased crystallinity at a low calcination temperature. Whiskers with larger diameters of 2 to 5 μm can be prepared by adding carbon powder to the intercalated compound complex.

BACKGROUND OF THE INVENTION

Carbides and nitrides, represented by silicon carbide and siliconnitride, possess excellent properties such as hardness, thermalconductivity, heat resistance, thermal shock resistance, and chemicalstability. They are being used increasingly as grinding and polishingmaterials, fire resistant materials, heating elements, electrical parts,and disoxidants. They are produced by calcining a mixture of a materialpowder and carbon under a reducing atmosphere or nitrogen gasatmosphere.

Silicon carbide is at present prepared as follows.

Alpha-silicon carbide powder is generally produced by filling a mixtureof silica and coke in an electric resistant furnace, heating the mixturewith application of electricity, and grinding and classifying theobtained crystalline lump.

To produce beta-silicon carbide, the following five methods have beenemployed.

(1) A direct reaction of silicon with carbon: A mixture of siliconpowder and fine carbon powder such as carbon black is calcined at atemperature in the range of 1000°-1400° C.

(2) Reduction reaction of silica with carbon: A mixture of silica powderand fine carbon powder is calcined at a temperature in the range of1500°-1800° C. under an inert atmosphere. This method is being employedin an industrial scale as a stable method for continuous mass productionwith use of a vertical reaction furnace.

(3) Vapor phase reaction: Hydrocarbon is reacted with silicontetrachloride or silicon tetrahydrogenate, or varying alkylsilanes aresubjected to thermal decomposition. This method is suitable to producemicronized powder of a particle size of less than 0.1 μm having highpurity and less aggregation. It, however, has various drawbacks, forexample, that the material gas is expensive and the used apparatus iscorroded by chlorides.

(4) Gas evaporation: The raw materials are heated at high temperature tobe evaporated and subjected to a reaction, and the prepared fineparticles are aggregated. It has been studied to employ a method ofdirectly passing electricity or making an arcing between a carbon rodand silicon. This method has not been put in practice.

(5) Thermal decomposition of organic silicon polymer: An organic siliconpolymer represented by polycarbosilane is thermally decomposed at atemperature more than 1500° C. under a non-oxidizing atmosphere. Sincethe material organic silicon polymer is quite expensive, this method isnot so suitable for the industrial production of beta-silicon carbidepowder.

As described above, silicon carbide is at present industrially producedby simply mixing material powders macroscopically and calcining theprepared mixture under a reducing atmosphere or an inert atmosphere.Other carbides or nitrides are prepared in the form of powder through amacroscopical contact of powder solids although the vapor phase reactionis employed when they are produced in the form of whisker. It may besummarized from the above that synthesis of carbide or nitride powderdepends on a reaction among solid particle surfaces of a materialmixture caused by calcination of the mixture at high temperature, or areaction of the sublimed gaseous components or a thermal decompositionreaction thereof. Consequently, the reaction must be carried out atamply high temperature under a reducing atmosphere or inert atmosphereto satisfactorily produce nitrides and carbides.

SUMMARY OF THE INVENTION

When compounds containing carbon and nitrogen atoms are present in everycrystal layer of the raw material, the reaction proceeds at a molecularlevel. The reaction can be carried out at a temperature more than 100°C. lower than that in a macroscopic mixing method. Besides, the yield ofcarbide and nitride is increased, and the crystallinity is improved.Accordingly, the present invention employs a method that a polarsubstance is intercalated into the interlamellar spaces of an inorganicmaterial having a lamellar structure to enlarge the interlamellarspaces; a starting material of polycondensate, a monomer, or aprepolymer is intercalated into the interlamellar spaces; and theresulting product is condensed or polymerized with a radical initiatorto form an inorganic-organic polymer intercalation compound. Thiscomplex is heated at 200°-250° C. to acquire flame resistant propertiesand baked at a temperature in the range of 1100°-1700° C. under areducing atmosphere or in a stream of inert gas.

DETAILED DESCRIPTION OF THE INVENTION

The substance to be intercalated into the interlamellar spaces may be aninorganic compound. Where a polymerized or condensed organic substanceis intercalated into the spaces, hydrocarbon and carbon monoxide formeddue to the thermal decomposition at high temperature keep the interiorof the reaction furnace under a reducing atmosphere, and the remainingcarbon becomes a raw material for carbide. Nitride can be suitablyproduced by calcining a compound containing nitrogen in an atmosphere ofnitrogen. The organic compound present in the interlamellar spacesgenerally evaporate at a temperature lower than 200° C. and disappearunless it is converted into a high-molecular compound. To prevent suchevaporation, a polymer is directly intercalated, or a monomer orprepolymer is intercalated and polymerized or condensed so that theevaporation does not take place until a temperature is raised high.

The present invention is novel on the following points.

(1) A prescribed organic compound and solvent are intercalated inadvance into the host interlamellar spaces of a lamellar structuredsubstance in order to enlarge the interlamellar spaces, so that a guestreaction substance can be easily entered into these spaces.

(2) An inorganic or organic guest reaction substance is intercalatedinto the enlarged host interlamellar spaces, so that the guest reactionsubstance contacts with the crystal faces of every layer of the hostcrystal and the reaction can be conducted microscopically.

(3) The guest reaction substance intercalated into the hostinterlamellar spaces is polymerized or condensed, so that the guestreaction substance is directly reacted with the host crystal faceswithout suffering evaporation of the reaction substance until itstemperature is raised high.

(4) The guest reaction substance is converted into a high-molecularcompound and subjected to a flame resistant treatment at a temperaturein the range of 200°-250° C. This treatment allows the intercalatedguest reaction substance to react until its temperature rises highwithout suffering evaporation and eliminates the organic substance whichis used to enlarge the interlamellar spaces of the host crystal. Sincethe decomposition product enhances the reducing atmosphere, the reactionreadily proceeds, the reaction temperature is lowered, the yield isincreased, and the crystallinity is increased.

A method for the production of silicon carbide and silicon nitride bycalcining a mere mixture of raw materials of 400 meshes (by Tylerstandard sieve; the same is applied throughout the specification) wascompared with the method of the present invention using syntheticpolysilicic acid. The test results indicate the superiority of thepresent invention as follows. The calcination could be done at atemperature low by 100°-200° C. to obtain the same yield; the yield wasincreased by 20-90% when the calcination was conducted at the sametemperature of 1100°-1600° C. for the same period of time; and it wasconfirmed by X-ray diffraction that the crystallinity was increased evenwhen the calcination was conducted at the same temperature for the sameperiod.

This invention will be explained below in detail.

(A) SYNTHESIS OF CARBIDES

Magadiite Na₂ Si₁₄ O₂₉ ·XH₂ O, one of lamellar polysilicates, is presentin nature but can be synthesized. The basal spacing of its crystallinelayers is 15.6Å and Na ions are present between the layers. Whenmagadiite is immersed in an aqueous alkyl ammonium solution, ionexchange takes place between Na ions and alkyl ammonium ions, formingmagadiite-alkyl ammonium intercalation compound. Because of the ionexchange between alkyl ammonium ions and Na ions, the basal spacingincreases to more than 20Å. This magadiite-organic complex is immersedin styrene monomer to prepare styrene-magadiite intercalation compound.To this compound is added a polymerization initiator to polymerizestyrene, thereby preparing magadiite-polystyrene intercalation compoundcomplex. It is confirmed by thermal analysis that styrene in an amountcorresponding to about 90 wt % of the amount of magadiite isintercalated into the interlamellar spaces though a little scattering inthe amount is observed depending on the preparation conditions. Themagadiite-polystyrene intercalation compound complex is then heated at atemperature in the range of 200°-250° C. to evaporate the unpolymerizedstyrene and the alkyl ammonium used to enlarge the interlamellar spaces,then the interlamellar spaces are contracted to connect fast the crystalface and styrene. The magadiite-polystyrene intercalation compoundcomplex thus provided with flame resistant properties is calcined at atemperature in the range of 1100°-1500° C. under a reducing atmosphereto produce silicon carbide.

Separately from the above method, a comparative experiment was conductedwith regard to a mixture of magadiite and polystyrene in the equalweight ratio. Magadiite of lamellar polysilicate magadiite was treatedwith an acid to remove sodium ions. The resulting lamellar polysilicatemagatiite was dried and reduced to powder of 400 meshes. The powder wasimmersed in a polystyrene-containing benzene solution in a weight equalto that of the powder, then agitated thoroughly to prepare a uniformmixture. The mixture was heated at 100° C. to evaporate benzene, therebypreparing a macroscopically uniform mixture of magadiite andpolystyrene. This magadiite-polystyrene mixture was once heated to200°-250° C. and calcined at a prescribed temperature. The resultantproduct was compared with the compound prepared by the aforesaid method.

The results revealed that when the calcination was conducted under areducing atmosphere at a temperature in the range of 1100°-1500° C. forthe same period of time, silicon carbide prepared by the method of thepresent invention had the yield larger by 30-80% than that of theproduct prepared from the above macroscopically uniform mixture; thetemperature required for the preparation of the equal amount of carbidewas lower in the case of using the intercalation compound complex by100°-150° C. than that required in the calcination of the abovemacroscopically uniform mixture; and the improvement of thecrystallinity was confirmed by sharpened peaks checked by X-raydiffraction. It is proved that in the method of calcining theintercalation compound complex according to the present invention,microscopical reaction takes place on every crystal face.

(B) SYNTHESIS OF NITRIDES

In the aforesaid method (A), the following is an example of using4-vinylpyridine as a guest organic substance.

Following the procedure of the above method (A), the interlamellarspaces of magadiite were enlarged with alkyl ammonium salt. Themagadiite was then immersed in a guest organic substance 4-vinylpyridinecontaining a polymerization initiator, and polymerized at 80° C. Theresulting product was subjected to flame resistant treatment at atemperature in the range of 200°-250° C. Thus, alkyl ammonium wasdecomposed and evaporated, forming magadiite-polyvinylpyridineintercalation compound complex. This complex was then calcined in astream of nitrogen gas at a temperature in the range of 1100°-1600° C.to form silicon nitride.

When this product was compared with that prepared by the calcination ofa magadiite-polyvinyl pyridine mixture, it was confirmed that the methodof the present invention increased the amount of silicon nitrideproduced by 20-80%; lowered the temperature for preparing the equalamount of silicon nitride by 100°-150° C.; and increased thecrystallinity as confirmed by X-ray diffraction. It is clear from theabove that a microscopical reaction took place on the crystal faces aswas in the above (A).

(C) SYNTHESIS OF CARBIDE, NITRIDE, AND SIALONS

Montmorillonite, one of 2:1 type clay minerals having a lamellarstructure, usually contains alkali metal ions such as sodium ion,potasium ion, etc. and alkaline earth metal ion such as calcium ion,magnesium ion, etc. as an exchangeable cation between the crystallinelayers. These ions are hydrated respectively. The interlamellar spacesare generally in the range of 2-6Å which varies depending on thehydrated degree. When the montmorillonite is dried to drive out thewater content, the spaces including cation columns are formed. And it ispossible to adjust an amount of exchangeable cations by pretreatmentwith an acid. Organic cations and various organic molecules take theplace of these inorganic cations in the interlamellar spaces and forintercalation compounds. Also, these interlamellar spaces can beenlarged by having organic solvents itercalated therein.

When the montmorillonite having the above features is treated with anaqueous alkylammonium salt solution, alkylamine montmorilloniteintercalation compound is formed as a result of intercalation ofalkylammonium ion. After washing, drying, and grinding, themontmorillonite organic complex is immersed in acrylonitrile monomer toprepare alkylamine acrylonitrile-montmorillonite intercalation compound.A polymerization initiator is added to the above compound to polymerizeacrylonitrile of the above compound, thereby obtainingmontmorillonite-polyacrylonitrile complex. The reason that thealkylamine montmorillonite complex is prepared in advance is tointercalate acrylonitrile monomer as much as possible into theinterlamellar spaces. Organic solvents such as benzene and toluene canbe employed to adjust the absorbed amount of acrylonitrile monomer or toenlarge the interlamellar spaces. Although a little difference isinvolved depending on the preparation conditions, thermogravimetricanalysis has confirmed that organic compounds in an amount correspondingto about 90 wt % of montmorillonite are intercalated into themontmorillonite.

Next, the montmorillonite-polyacrylonitrile complex is heated at200°-250° C. to cyclize the polyacrylonitrile which is present in theinterlamellar spaces, thereby giving flame resistant properties to thecomplex so that the polyacrylonitrile does not evaporate at hightemperature. The resulting montmorillonite-polyacrylonitrile complex isburned to a temperature over 1100° C. in an inert gas or under areducing atmosphere to obtain nitride, carbide, and sialons.

Since the montmorillonite contains preponderantly SiO₂ and Al₂ O₃ and asmall amount of Fe₂ O₃, MgO, CaO, Na₂ O, and K₂ O, pure carbide ornitride cannot be prepared by the calcination ofmontmorillonite-polyacrylonitrile intercalation compound. In addition tothe above carbide and nitride, beta-sialon and aluminum nitride areprepared simultaneously.

The results obtained by the comparison of the temperature used for thepreparation of the product by the method of this invention with thatused for the preparation of the calcination product of themontmorillonite-polyacrylonitrile mixture are as follows.

The production of beta-sialon was initiated when the temperature was1100° C. in the case of the calcination product of the intercalationcompound complex while it was 1300° C. in the case of the calcinationproduct of the mixture; the production of bata-carbide was initiated at1150° C. in the former case and 1250° C. in the latter case; theproduction of aluminum nitride was initiated at 1300° C. in the formercase and 1500° C. in the latter case; and the production of beta-siliconnitride was initiated at 1400° C. in the former case and 1500° C. in thelatter case. It is clear from the above that the production temperaturewas lowered by 100°-200° C. When the calcination temperature is thesame, the present invention increases the content of the above compoundsproduced. X-ray diffraction confirmed that the crystallinity of eachcompound was increased when prepared by calcining the intercalationcompound complex as compared with that prepared by calcining themixture. It was confirmed from the above that the product prepared byintercalating an inorganic or organic compound into the interlamellarspaces of a compound, polymerizing or condensing the intercalationproduct, conducting a flame resistant treatment, and calcining at atemperature in the range of 1100°-1600° C., is superior to the productprepared by calcination of a mixture in the calcination temperature,yield, and crystallinity because of the microscopical reaction of thecrystal faces.

It is also possible to prepare whiskers efficiently by the method ofthis invention. Whiskers of silicon carbide and silicon nitride now onthe market are produced by a vapor phase reaction of CO or N₂ gas withSiO gas formed by reducing SiO₂. At any rate, when one of the reactingcomponents is a solid, silicon carbide or silicon nitride is formed inthe form of powder.

As described above, silicon carbide and silicon nitride are prepared bycalcining an intercalation compound complex which is prepared byintercalating an inorganic or organic compound into interlamellar spacesand polymerizing or condensing the resulting product; the abovecalcination is carried out at a temperature 100°-200° C. lower than thatfor the calcination of a mere mixture; and the yield and crystallinityare increased.

Similar tendency is observed in the production of whiskers and whencarbon powder is added to an intercalation compound complex, whiskersare more readily produced. Whiskers heretofore produced have a diameterof 0.1-1 μm. The present invention has a characteristic feature ofproducing whiskers having a diameter of 2-5 μm. This fact is confirmedby an electron microscope photograph. When these whiskers areincorporated into metals and plastics, the metals and plastics havetheir strength enhanced greatly than the conventional whiskers are used.

Instead of the montmorillonite used above, the following inorganiccompounds may be used as the host crystalline starting materials. Theyare lamellar clay minerals such as kaolinite, halloysite, vermiculliteand others, fibrous clay minerals (inosilicate) such as sepiolite andattapulgite, and natural or synthetic minerals such as zeolite(tectosilicate) having a three dimensional network structure such asclinoptilolite, mordenite, etc. It is also possible to use any compoundwhich includes polisilicic acid having a lamellar structure, graphite,chalcogen compounds, oxide, oxyhalogen compounds, black phosphorous,zirconium phosphate, inorganic compounds of transition metal oxyacidsalts, and synthetic zeolite having a three dimensional networkstructure.

The organic compounds which enlarge the interlamellar spaces orintercalate into the three dimentional network crystal spaces includethe polar compounds such as butylamine, hexylamine, dodecylamine,octadecylamine, benzylamine, and other alkylamines, and amides such asformamide, acetamide, etc. Even a nonpolar organic compound can beintercalated into the spaces when the immersing conditions are suitable.

Preferable solvents are benzene, toluene, xylene, pyridine, and otherscontaining carbon atom or nitrogen atom. Examples of the monomersinclude acrylonitrile, styrene, acrylic acid, methacrylic acid, methylmethacrylate, vinyl pyridine, etc. The preferable primary condensationpolymerization products or prepolymers are urea resin, phenol resin andothers, which are not volatilized by heating in the course ofpolymerization or polycondensation process. In the interlamellar spacesthey react with the crystal faces at a molecular level at hightemperature to form carbides or nitrides.

The present invention will be understood more readily by reference tothe following examples; however, these examples are intended toillustrate the invention and are not to be construed to limit the scopeof the invention.

EXAMPLE 1

Magadiite, a lamellar state of polysilicic acid, was prepared by thefollowing method. Amorphous silica and 10% sodium hydroxide aqueoussolution were mixed to give the proportional of chemical composition ofSiO₂ 27, Na₂ O 3, and H₂ O 70 in percent by weight. The obtained mixturewas heated at 100° C. for 48 hours. The reaction product was washed withNaOH aqueous solution (PH=9), and air-dried to form magadiite.

The magadiite thus produced was analyzed by X-ray diffraction. Then itwas immersed in 0.01N-HCl aqueous solution, followed by filtration anddrying. One hundred grams of the obtained magadiite were immersed in 300ml of 0.2 mol stearyltrimethylammonium aqueous solution for 24 hours toexchange the sodium ion present in the magadiite interlamellar spaceswith stearyltrimethylammonium ion. As a result, there was producedmagadiite-stearyltrimethylammonium intercalation compound.

The increase of the basal spacing from 15.6Å in the starting magadiiteto 28Å in the obtained compound confirmed the intercalation ofstearyltrimethylammonium ion. This compound was immersed in 300 ml ofstyrene monomer containing 1% of azobisisobutyronitrile as a radicalinitiator for 48 hours to intercalate the styrene monomer into theinterlamellar spaces of the compound, thereby producingmagadiite-styrene intercalation compound. This compound was thenfiltered and heated at 90° C. for two hours to polymerize the styrenemonomer. The resultant product was heated at 200° C. for two hours toacquire flame resistant properties, thereby preparingmagadiite-polystyrene intercalation compound complex. This complex wascalcined in a stream of hydrogen at a temperature 1400° C. for threehours to form silicon carbide. Silicon carbide content was more than95%, indicating that the amount of silicon carbide prepared wasincreased by 80% as compared with that obtained by calcining under thesame conditions a mixture of magagiite and polystyrene in the sameweight ratio. It was confirmed by X-ray diffraction that the calcinationproduct of the complex had a higher crystallinity than that of thecalcination product of the mixture.

EXAMPLE 2

One hundred grams of the magadiite prepared in Example 1 were immersedin 300 ml of dimethylformamide for 48 hours to intercalate into themagadiite dimethylformamide in an amount equal to 90 wt % of themagadiite, resulting in the production of dimethylformamide complex.This complex was immersed in 300 ml of 4-vinylpyridine containing 1% ofazobisisobutyronitrile as a radical initiator for 48 hours tointercalate 4-vinylpyridine, thereby preparingmagadiite-dimethylformamide-4-vinylpyridine intercalation compound. Thiscompound was heated at 80° C. for three hours to polymerize and, thenheated at 200° C. for two hours to acquire flame resistant properties,thereby preparing magadiite-polyvinylpyridine intercalation compound.This compound was calcined in a stream of nitrogen of 300 ml/min at 1400° C. for three hours to prepare silicon nitride. Its content was morethan 95%. When the silicon nitride was compared with the calcinationproduct of the magadiite-polyvinylpyridine mixture, the amount ofsilicon nitride was increased by 80%. It was also confirmed by X-raydiffraction that the crystallinity of the silicon nitride was higherthan that of the calcination product of the mixture.

EXAMPLE 3

Montmorillonite, produced at Aterazawa, Yamagata Prefecture, Japan, wasused as a starting material for the intercalation compound. It wasnatural clay having a lamellar structure. It was purified by elutriationand subjected to X-ray diffraction and thermal analysis to ascertainthat it was montmorillonite. Its chemical compositions were SiO₂ 57%,TiO₂ 0.01%, Al₂ O₃ 21.9%, Fe₂ O₃ 1.92%, MgO 3.50%, CaO 0.63%, Na₂ O2.85%, K₂ O 0.17%, H₂ O (+) 5.80%, and H₂ O (-) 5.10%. Thecation-exchange capacity was 84.5 milliequivalents/100 grams.

One hundred grams of this montmorillonite were immersed in one liter of0.2 N dodecylammonium hydrochloride aqueous solution to exchange sodiumions present in the interlamellar spaces with dodecyl ammonium ions.This operation was repeated twice so that the ammonium ion wasintercalated sufficiently into the interlamellar spaces. The resultantproduct was washed with water and dried to preparemontmorillonite-dodecylammonium ion intercalation compound complex.

The above complex was immersed in 300 ml of acrylonitrile monomercontaining 0.7% by weight of benzoylperoxide as a polymerizationinitiator for 24 hours to fully intercalate the acrylonitrile monomerinto the montmorillonite interlamellar spaces. The product was filteredto remove excess acrylonitrile monomer, then heated at 50° C. for 24hours to undergo polymerization to formn-dodecylammonium-montmorillonite-polyacrylonitrile intercalationcompound. The enlargement of the interlamellar spaces of themontmorillonite from 13.5Å to 25.6Å confirmed the intercalation ofpolyacrylonitrile.

The obtained complex was then heated at 220° C. for two hours to acquireflame resistant properties. The flame resistant complex obtained wasfree from volatilization even when subjected to calcination at hightemperature and gave carbides and nitrides by the reaction ofpolyacrylonitrile with the crystal face of montmorillonite at amolecular level. Calcination was carried out in a stream of nitrogenwith a gas flow rate of 500 ml/min at 1400° C. for six hours. There wereprepared beta-sialon at 1100° C., beta-silicon carbide at 1150° C.,beta-silicon nitride at 1400° C., and aluminum nitride at 1300° C. Thesetemperatures were 100°-200° C. lower than those in the calcination ofthe montmorillonite-polyacrylonitrile mixture. Their yields were alsoincreased. It was confirmed by X-ray diffraction that the crystallinitywas increased.

EXAMPLE 4

Kaolinite having a lamellar structure and being a 1:1 type clay mineralwas subjected to X-ray diffraction and thermal analysis to ascertainthat it was kaolinite. One hundred grams of kaolinite were immersed in300 ml of N, N-dimethylformamide for 24 hours.

The increase of the basal spacing from 7.2Å to 12Å obtained by the abovetreatment confirmed that dimethylformamide was intercalated into theinterlamellar spaces of kaolinite.

The amount of dimethylformamide absorbed by kaolinite was equal to 90%by weight of the kaolinite. The produced kaolinite-dimethylformamidecomplex was filtered to remove excess dimethylformamide, and immersed in300 ml of styrene monomer containing 1% of azobisisobutyronitrile as apolymerization initiator for 24 hours to exchange the dimethylformamideas a host molecule contained in the interlamellar spaces with styrenemonomer as a guest molecule. After filtering off excess styrene monomer,the obtained complex was polymerized by heating at 100° C. for two hoursto form kaolinite-polystyrene intercalation compound. It was confirmedby IR absorption spectrum analysis that polystyrene was intercalatedinto the interlamellar spaces of kaolinite.

When the complex was heated at 250° C. for two hours to acquire flameresistant properties, evaporation of dimethylformamide and contractionof the interlamellar spaces took place, thereby prepared waskaolinite-polystyrene intercalation compound complex due to fast contactof the crystal faces and polystyrene at a molecular level. This complexwas calcined in a stream of nitrogen at 1500° C. for two hours. By thereaction of the unit crystal with polystyrene at a molecular level,silicon carbide, silicon nitride, and beta-sialon were formed. Acompound prepared by the calcination of a complex according to thepresent invention was calcined at a temperature 100°-200° C. lower thanthat used for the calcination of a kaolinite-polystyrene mixture. It wasconfirmed by X-ray diffraction that the yield and crystallinity wereincreased.

EXAMPLE 5

Five hundred ml of a 0.5N hydrochloric acid was added to 100 g of aklalititanic acid, Na₂ Ti₃ O₇ or K₂ Ti₄ O₉, having a lamellar structure. Themixed solution was reacted at 70° C. for 24 hours to remove alkalimetal. After filtering, 500 ml of 50% n-propylamine solution was addedand treated at 70° C. for 48 hours to intercalate n-propylamine ion intothe interlamellar spaces. The titanium oxide-propylamine intercalationcompound complex obtained was immersed in 300 ml of acrylic acidcontaining 1% of benzoylperoxide as a polymerization initiator for 24hours. As a result, propylamine present in the interlamellar spaces wasexchanged with acrylic acid as a guest molecule. The resultant productwas filtered, and heated at 85° C. for two hours to polymerize acrylicacid, thereby forming an intercalation compound of titaniumoxide-polyacrylic acid in which the polyacrylic acid had beenintercalated into the interlamellar spaces of titanium oxide. Theintercalated polyacrylic acid was confirmed by IR absorption spectrumanalysis.

The obtained intercalation compound was ground, and calcined in a streamof nitrogen or under a reducing atmosphere at 1500° C. for two hours.Thus, titanium carbide was formed by the reaction of polyacrylic acidwith the crystal face of titanium oxide at a molecular level. Theprepared amount of titanium carbide was increased by 80% as comparedwith the product obtained by the calcination of the titaniumoxide-polyacrylic acid mixture under the same conditions.

EXAMPLE 6

To sodium metavanadate solution was added a dilute hydrochloric acid inan amount slightly excess of equivalence to exchange Na ions with Hions, thereby preparing a vanadic acid solution. This solution was agedat 50° C. for 48 hours to prepare dark-red vanadium pentoxide hydratehaving a lamellar structure. X-ray diffraction showed that the basalspacing of the vanadium pentoxide hydrate was 8.75Å. One hundred gramsof vanadium pentoxide hydrate dried in air were immersed in 200 ml of a50% ethylene glycol solution for 24 hours while stirring. As a result,the basal spacing was enlarged to 17Å. After filtering, the resultingcomplex was immersed in 300 ml of acrylic acid monomer containing 1.0%of benzoyl peroxide for 24 hours, thereby thoroughly intercalatingacrylic acid monomer into the interlamellar spaces of vanadiumpentoxide. After removing excess acrylic acid monomer by filtration,polymerization was conducted at 80° C. for three hours to prepareethylglycol type vanadium pentoxide-polyacrylic acid intercalationcompound complex.

The complex was heated at 220° C. for two hours to drive out ethyleneglycol and to conduct flame resistant treatment. The resulting flameresistant complex was reacted with polyacrylic acid on the crystal faceof vanadium pentoxide at a molecular level and formed vanadium carbideunder a reducing atmosphere. For example, vanadium carbide can beproduced by calcining the above complex at 1400° C. for five hours in astream of CO gas of 300 ml/min. The above temperature was 150° C. lowerthan that required for the calcination of a vanadiumpentoxide-polyacrylic acid mixture under the same conditions. When thecalcination temperature was identical, the yield was increased by 90%.X-ray diffraction confirmed that the crystallinity was also increased.

EXAMPLE 7

The vanadium pentoxide hydrate having a lamellar structure prepared inExample 6 was immersed in 200 ml of a 1N N-methylacetamide for 24 hourswith occasional stirring to enlarge the basal spacing from 8.75Å to 19Å.After filtering, the resulting substance obtained was immersed in 300 mlof 4-vinylpyridine monomer containing 1.0% of benzoyl peroxide for 24hours to intercalate 4-vinylpyridine monomer, thereby preparingN-methylacetamide type vanadium pentoxide-4-vinylpyridine intercalationcompound. After filtration, the resulting compound was heated at 90° C.for two hours to polymerize 4-vinylpyridine monomer. This complex washeated at 220° C. for two hours to release N-methylacetamide and prepareflame resistant vanadium pentoxide-polyvinyl pyridine intercalationcompound complex. This complex was calcined at 1400° C. for five hoursin a stream of nitrogen gas of 300 ml/min to prepare silicon nitride.Its purity was more than 90%.

The above silicon nitride was 85% greater in the yield than that of theproduct prepared by calcining a mixture of vanadium pentoxide andpolyvinyl pyridine under the same conditions. X-ray diffractionconfirmed that the crystallinity was also higher than that of theproduct from the mixture.

EXAMPLE 8

One hundred grams of molybdenum sulfide, a lamellar structure ofdichalcogen compound, were immersed in 300 ml of pyridine for two hoursto intercalate the pyridine molecules into the intermalellar spaces.Molybdenum sulfide-pyridine complex obtained by filtration was immersedin 300 ml of acrylonitrile monomer containing 1% of benzoylperoxide as apolymerization initiator for 24 hours to prepare molybdenumsulfide-acrylonitrile complex. The acrylonitrile contained in thiscomplex was polymerized at 60° C. to prepare an intercalation compoundof molybdenum sulfide-polyacrylonitrile.

The obtained compound was heated at 225° C. for 20 hours to acquireflame resistant properties. By this treatment, pyridine was evaporatedand the interlamellar spaces were contacted. As a result, there wasprepared molybdenum sulfide-polyacrylonitrile compound complex where thecrystal faces and polyacrylonitrile were adhered tight at a molecularlevel. Calcination of the resultant compound in a stream of nitrogen at1500° C. for two hours caused a reaction of polyacrylonitrile with thecrystal faces of molybdenum sulfide at a molecular level to preparemolybdenum nitride. The amount of molybdenum nitride obtained wasincreased by 70% as compared with that obtained by calcining a mixtureof molybdenum sulfide and polyacrylonitrile. It was also confirmed byX-ray diffraction that the crystallinity was increased.

EXAMPLE 9

One hundred grams of clinoptilolite (produced at Itaya, YamagataPrefecture, Japan), a kind of tectosilicates having a three dimensionalnetwork structure, were heated at 500° C. for one hour to drive outwater from its pores. The resulting dehydrated clinoptilolite wasimmersed for 24 hours in a solution which was prepared by mixing 50parts of urea, 100 parts of formaline, and 0.5 part of aqueous ammonia.The resultant product was filtered, and reacted at 90° C. for one hourto prepare a product of clinoptilolite-urea resin precondensate. Theabove product was thoroughly kneaded with oxalic acid, heated at atemperature in the range of 80°-90° C. to form a bulk compound, and thisbulk compound was ground to prepare a complex of clinoptilolite-urearesin. The resultant complex was gradually heated in a stream ofnitrogen to calcinate at 1400° C. for two hours, thereby obtainingbeta-sialon, silicon carbide, aluminium nitride, and silicon nitride.Their amounts thus obtained were increased by 70% as compared with thatobtained by calcining a mere mixture of clinoptilolite and urea resin.It was also confirmed by X-ray diffraction that their crystallinitieswree increased.

EXAMPLE 10

One hundred grams of attapulgite, one of inosilicates having a fibrousstructure, were heated at 500° C. for one hour to drive out the watercontent from prismatic spaces of the attapulgite crystalline structure.The dehydrated attapulgite was immersed for 24 hours in a solution whichwas prepared by mixing 15 parts of phenol, 15 parts of formalin, and 0.5part of aqueous ammonia. Then, the mixture was filtered, and heated fortwo hours until it was boiled to prepare phenol resin, thereby producingattapulgite-phenol resin complex.

The prepared complex was dehydrated at 75° C. under reduced pressure of30 mmHg and cooled down to form a sample for calcination. This samplewas mixed with 5% by weight of graphite powder, and the mixture wasfinely divided and heated gradually in a stream of nitrogen of 500ml/min at 1400° C. for two hours to form silicon carbide, siliconnitride, aluminum nitride, and beta-sialon. Their amounts thus obtainedwere increased by 75% as compared with that obtained by calcining a meremixture of attapulgite and phenol resin. It was also confirmed thattheir crystallinities were increased.

EXAMPLE 11

Magadiite-polystyrene intercalation compound complex prepared accordingto the procedure of Example 1 was pulverized to a size of 400 meshes.The pulverized complex was mixed with 50 wt % of graphite powder andheated at 200° C. for two hours to acquire flame resistant properties.The resulting product was calcined at 1500° C. for three hours in astream of carbon monoxide of 300 ml/min to prepare whiskers in an amountequal to 60% of the starting material. When the obtained whiskers wereobserved through an electronic microscope, their diameters were about 5μm which was 5-50 times greater than those of the conventional whiskers,indicating their strengths were increased.

What is claimed is:
 1. A method for the preparation of nitrides andcarbides comprising intercalating at least one member selected from thegroup consisting of a monomer, a starting material of polycondensate, ora prepolymer into the interlamellar spaces of natural minerals orinorganic compounds having a lamellar structure, preparing anintercalated compound by inducing polymerization or polycondensation ofthe at least one member, and baking the intercalated compound at atemperature in the range of 1100°-1700° C. under a nitrogen or reducingatmosphere.
 2. A method for the preparation of nitrides and carbidescomprising intercalating at least one member selected from the groupconsisting of a monomer, a starting material of polycondensate, or aprepolymer into the vacant spaces of the crystalline structure ofnatural or synthetic inosilicates having fibrous structure or into thoseof the crystalline structure of natural or synthetic tectosilicateshaving three dimensional network structure, preparing aninorganic-organic polymer complex by inducing polymerization orpolycondensate of the at least one member, and baking theinorganic-organic polymer complex at a temperature in the range of1100°-1700° C. under a nitrogen or reducing atmosphere.